1. Field of the Invention
The present invention relates to a thermal recording material on which information is recorded through thermal deformation by irradiation with a beam of high energy density radiation. In greater detail the present invention relates to a thermal recording material in which a subbing layer containing both chlorinated polyolefin and an aminoalkylalkoxysilane compound between the support and the recording layer. The subbing layer can contribute to improvements in the sensitivity of the recording material and adhesion between the support and the recording layer.
2. Description of the Prior Art
Recording materials utilizing high energy beam of light such as a laser and the like, there have been known including thermal recording materials as described below in addition to silver salt-containing light sensitive materials. A thermal recording material generally comprises a recording layer of high optical density such that areas irradiated with a high energy density light beam produce local increases in temperature which result in thermal deformation such as fusion, evaporation, aggregation and so on and a difference in optical density results between the optically exposed areas and the optically unexposed areas. Thermal recording materials such as this possess several advantages. They do not require any developing and subsequent fixing. They make processings in a dark room unnecessary because of their insensitivity to ordinary indoor light. They can provide images of high contrast and they make it possible to put additional information on record (generally referred to as "add-on"), and so on.
Many of the processes for recording information on this type thermal recording material include, in general, the steps of transforming the information into electrical time series signals and scanning the recording material with a laser beam modulated in its amplitude according to such signals. These processes have an advantage that images can be recorded in real time.
The materials generally constituting the recording layers of thermal recording materials are metals, dyes, plastics and the like. It is generally possible to choose low-priced materials. The recording materials as described above are described in more detail in, for example, M. L. Levene, et al., Electron, Ion and Laster Beam Technology, transactions of 11th symposium (1969); Electronics, Mar. 18, 1968, page 50; D. Maydan, The Bell System Technical Journal, vol. 50 (1971), page 176; C. O. Carlson, Science, vol. 154 (1966), page 1550; and so on. Of these materials, those which utilize metals as recording layers, wherein thin layers of metals such as Bi, Sn, In and the like are, for example, laminated on supports, possess excellent characteristics as the thermal recording materials because images can be recorded thereon with high resolving power and high contrast.
However, recording materials utilizing thin metal layers suffer, in general, from the defect that generally 50% or more of the laser beam employed for recording is reflected from the thin metal layer and, therefore, the energy of the laser beam is not used effectively and a high power beam is required for recording. This is especially the case when rapid scanning where still higher power is required and, consequently, the apparatus becomes large and expensive.
Under these circumstances, some recording materials having high recording sensitivity have been investigated. As an example thereof, Japanese Patent Publication No. 40479/'71 propose a recording material of a triple-layer construction of Se, Bi and Ge in which a very thin layer of Ge is laminated on a thin layer containing Se and Bi to reduce reflectance. However, the use of Se is undesirable because it tends to cause pollution problems.
Another example of the recording material having a reflection preventing layer is described in Japanese Patent Application (OPI) No. 74632/'76, wherein a reflection preventing layer capable of absorbing light in the wave length region of the laser beam used for recording is provided on a metal layer. However, it is very difficult to get rid of light reflection completely by providing a reflection preventing layer on the metal layer. Even if it becomes possible to eliminate light reflection completely, the light source is often required to have high power in order to cause thermal deformation such as fusion, evaporation, aggregation or the like in the thin metal layer, as compared to that required for recording an image in a silver halide photosensitive material or an electrophotographic material.
In addition, recording layers of thermal recording materials and especially metal layers are liable to scratch. Therefore, a protecting layer is provided on the recording layer to improve durability, mechanical strength and keeping stability. The characteristics indispensable for the protecting layer are high transmittance with respect to a light beam of high energy density, high mechanical strength, low reactivity with a recording layer, good coating quality, facility in preparation and so on.
Substances employable for making the protecting layers may be either inorganic or organic compounds. Examples of inorganic compounds are transparent substances such as Al.sub.2 O.sub.3, SiO.sub.2, SiO, MgO, ZnO, MgF.sub.2, CuF.sub.2 and the like. On the other hand, the use organic substances is disclosed, for example, in each of Japanese Patent Applications (OPI) Nos. 96716/'74, 59626/'76, 75523/'76, 88024/'76 and 134633/'76. However, in recording materials having protecting layers as described above, the recording sensitivity decreases to a great extent, compared with those which do not have any protecting layers.
As described above, there is a need in this art to improve recording speed, reduce the size of the recording apparatus and the price thereof, to give practical sensitivity to a recording material even when a protecting layer having sufficient protecting ability is provided thereon, therefore, various investigations have been undertaken to obtain highly sensitive thermal recording materials.
As an example of investigation undertaken to improve the recording sensitivity, mention may be made of the Japanese Patent Application No. 77269/'78 (corresponding to U.S. patent application Ser. No. 52,277 filed June 26, 1979), in which a subbing layer containing chlorinated polyolefin is provided between a recording layer and a support for this purpose. Though the reason for the improvement in recording sensitivity brought about by the chlorinated polyolefin layer provided between the recording layer and the support is still not completely clear, it may be because the chlorinated polyolefin melts at a lower temperature than the recording layer does, the deformation of the recording layer can be accelerated by the melting of the chlorinated polyolefin. However, the adhesion between the recording layer and the support (namely the degree of difficulty arising in delamination of the recording layer from the support) is not changed, or is deteriorated to some extent by providing the chlorinated polyolefin layer, compared with the case that the chlorinated polyolefin layer is not provided therebetween. Therefore, depending upon handling or usage of the recording material, sometimes the adhesion is not sufficient. In addition, when a protecting layer is formed on the recording layer using a coating technique, a solvent contained in the coating solution can permeate into the recording layer to reach the chlorinated polyolefin layer. Under such a condition, the chlorinated polyolefin can be dissolved, and through such a dissolution cracks appear in the recording layer or the uniformity of the recording layer deteriorates. Accordingly, the solvent of the coating solution used for making the protecting layer can not be freely chosen which also restricts the choice of substances for the protecting layer since they must have high solubility in a given solvent and that, solvent must be readily removed at the time of drying from the coated protecting layer.